scholarly journals Experimental Investigation of Wave-Induced Hydroelastic Vibrations of Trimaran in Oblique Irregular Waves

2016 ◽  
Vol 2016 ◽  
pp. 1-17 ◽  
Author(s):  
Haoyun Tang ◽  
Huilong Ren ◽  
Hui Li ◽  
Qi Zhong
Keyword(s):  
Longitudinal Vibration ◽  
Model Tests ◽  
Irregular Waves ◽  
Wave Impact ◽  
Wave Condition ◽  
Strength Assessment ◽  
Irregular Wave ◽  
Hydroelastic Vibrations ◽  
Structural Parts ◽  
Wave Induced

The irregular wave condition, especially the oblique irregular wave condition, is the actual circumstances when trimaran is sailing in sea. In order to identify the characteristic of the wave-induced hydroelastic vibration in irregular waves, as well as investigate the change of vibration in different oblique irregular wave conditions, trimaran model tests were conducted to measure vibrations, wave impact, and motion under different azimuth and wave height. The vibration on main hull, side hull, and cross-desk is measured and analyzed separately to observe the influence of irregular wave in different structural parts. The longitudinal vibration, transverse vibration, and torsion are also included in the model tests measurement to investigate the relationship between these vibration deformation components and parameters of the irregular waves. The wave-induced hydroelastic vibrations and whipping effect is extracted and analyzed to find influence of whipping and springing on the total vibration. Based on the analysis, the dangerous positions and the critical waves condition is introduced to ensure that the subsequent structural strength assessment is more reliable.

Green Water on FPSO Predicted by a Practical Engineering Method and Validated Against Model Test Data for Irregular Waves

2014 ◽  
Author(s):  
Rafael Vergara Schiller ◽  
Csaba Pâkozdi ◽  
Carl Trygve Stansberg ◽  
Douglas Gustavo Takashi Yuba ◽  
Daniel Fonseca de Carvalho e Silva
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Irregular Waves ◽  
Green Water ◽  
Wave Impact ◽  
Irregular Wave ◽  
Beam Seas ◽  
Practical Engineering ◽  
The University ◽  
Wave Induced

This paper presents a series of numerical analyses performed with the potential theory-based Green Water engineer tool KINEMA3. KINEMA3 was designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in design load analysis. The purpose of the study presented herein is to validate KINEMA3 green water (deck overtopping) predictions in nonlinear irregular waves with results from model tests performed at the TPN (Tanque de Provas Numérico) laboratory at the University of São Paulo, Brazil. Comparisons are made for a selection of irregular wave cases, for two choices of anchoring conditions (free floating vessel and fixed vessel) and for three wave headings (180°, 225° and 270°: head, quartering and beam seas, respectively). KINEMA3 statistical green water predictions present a general good agreement with observations from the TPN model tests for all wave cases, headings and mooring conditions. Overall, observed trends for occurrence of green water and standard deviation/maximum of relative wave height are successfully reproduced by KINEMA3. In agreement with model test results, it is predicted that green water occurs more frequently for a free floating vessel and for beam seas. Additional comparisons between KINEMA3 predictions using different FPSO panel models (low-order and high-order models) present negligible differences with respect to green water estimates. The results presented herein demonstrate the robustness of the tool towards the prediction of green water for variable wave headings and sea states, and highlight the capability of KINEMA3 to be employed as an engineering-like tool for fast and multiple estimates of green water in early design studies. This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.

Resonant Vibrations of Riser Guide Tubes Due to Wave Impact

2004 ◽  
Author(s):  
Arne Nestega˚rd ◽  
Arve Johan Kalleklev ◽  
Kjell Hagatun ◽  
Yu Lin Wu ◽  
Sverre Haver ◽  
...  
Keyword(s):  
High Frequency ◽  
Rapid Change ◽  
Ocean Basin ◽  
Model Tests ◽  
Slender Body ◽  
Irregular Waves ◽  
Resonant Vibrations ◽  
Wave Impact ◽  
Numerical Predictions ◽  
Steep Waves

The Kristin platform is a catenary moored semi-submersible production vessel (SSPV) intended for production of gas at the Kristin field at Haltenbanken. Kristin has 24 riser guide tubes for tie in of flexible risers, umbilicals and electric cables to the riser balcony. The riser guide tubes (RGT) provide the necessary guiding, support and protection for risers and cables. The guide tubes run vertically from the deck and through the extended east pontoon. The guide tubes are welded to the pontoon and horizontally supported at the underside of the balcony deck. During model tests of the Kristin platform performed in the Ocean Basin laboratory at Marintek, high frequency in-line vibrations of the RGTs were observed during passage of steep waves. The resonance period for the individual RGTs is 0.3 sec. To mitigate the vibration problem, a vibration suppression arrangement of stiff rods was introduced between the guide tubes. Model tests were performed with respect to extreme- and fatigue loads in regular and irregular waves, with and without the suppression arrangement. The model included the floating framework representing the hull and the 24 RGTs with correct diameter and resonance period. The model was suspended in a horizontal mooring system, giving resonance periods in surge and sway close to the prototype platform. A load-response model for the interaction between large steep waves and vertical flexible cylinders has been developed. A slender body load model derived from Morison’s equation is shown to be able to excite the resonant vibrations. The dominant part of the loading comes from the rapid change of added mass momentum, giving rise to an additional slamming term in the load formulation. The structural response is calculated from a recognized non-linear slender body response program. Numerical simulations have been carried out and compared with model tests for both regular and irregular waves. The numerical predictions confirm the effect observed in the model tests; i.e. connecting the tubes generally leads to a reduction of the high frequency response amplitudes.

scholarly journals A Phenomenological Study of Lab-Scale Tidal Turbine Loading under Combined Irregular Wave and Shear Flow Conditions

2021 ◽  
Vol 9 (6) ◽  
pp. 593
Author(s):  
Matthew Allmark ◽  
Rodrigo Martinez ◽  
Stephanie Ordonez-Sanchez ◽  
Catherine Lloyd ◽  
Tim O’Doherty ◽  
...  
Keyword(s):  
Shear Flow ◽  
Phenomenological Study ◽  
Spectral Characteristics ◽  
Irregular Waves ◽  
Flow Structures ◽  
Wave Impact ◽  
Power Extraction ◽  
Irregular Wave ◽  
Cross Covariance ◽  
The Impact

Tidal devices are likely to faced with shear flows and subjected to various wave climates. The paper presents an experimental study of the combined impacts of shear profile and irregular waves on the loading of a 1/20th scale device operating at peak power extraction. The experiments presented were conducted at various depths to facilitate analysis of the effects of the shear flow and wave impact on the device at various positions in the water column. The fluid field was measured at three different upstream positions and at three depths (top, middle and bottom of the rotor) for each experiment; in doing so, data from the device were captured three times. The fluid measurements were of a high quality and were analysed to present the structure flow upstream of the device, which contained velocity and turbulence profiles. The upstream measurement was utilised to understand the development of flow structures in the approach to the device, and the impact of the flow structures measured was confirmed via cross-covariance calculations. The long datasets gathered were used to produce full rotational probability density functions for the blade-root-bending moments for three blades. The spectral characteristics were also considered, and showed that rotor loading quantities are less reactive to smaller scale flow structures.

scholarly journals Meshless Model for Wave-Induced Oscillatory Seabed Response around a Submerged Breakwater Due to Regular and Irregular Wave Loading

2020 ◽  
Vol 9 (1) ◽  
pp. 15
Author(s):  
Dong-Sheng Jeng ◽  
Xiaoxiao Wang ◽  
Chia-Cheng Tsai
Keyword(s):  
Theoretical Models ◽  
Irregular Waves ◽  
Degree Of Saturation ◽  
Submerged Breakwater ◽  
Soil Response ◽  
Irregular Wave ◽  
Mesh Free ◽  
Low Degree ◽  
Height Increase ◽  
Wave Induced

The evaluation of wave-induced seabed stability around a submerged breakwater is particularly important for coastal engineers involved in design of the foundation of breakwaters. Unlike previous studies, a mesh-free model is developed to investigate the dynamic soil response around a submerged breakwater in this study. Both regular and irregular wave loadings are considered. The present model was validated against the previous experimental data and theoretical models for both regular and irregular waves. Parametric study shows the regular wave-induced liquefaction depth increases as wave period and wave height increase. The seabed is more likely to be liquefied with a low degree of saturation and soil permeability. A similar trend of the effects of wave and seabed characteristics on the irregular wave-induced soil response is found in the numerical examples.

Green Water and Wave Impact on FPSOs in Santos Basin: Challenges and Prediction Tools

2014 ◽  
Author(s):  
Rafael Vergara Schiller ◽  
Csaba Pâkozdi ◽  
Carl Trygve Stansberg ◽  
Daniel Fonseca de Carvalho e Silva
Keyword(s):  
Wave Structure ◽  
Sensitivity Study ◽  
Irregular Waves ◽  
Green Water ◽  
Wave Impact ◽  
Wave Amplification ◽  
Campos Basin ◽  
Water Problem ◽  
In Transit ◽  
Wave Induced

Green water (water-on-deck) and subsequent wave impact is a strongly non-linear, random and complex phenomenon that represents an important factor to be considered in the design of moored vessels and vessels in transit. The Santos Basin, in southeast Brazil, is a new frontier for deep water oil production, where FPSO green water issues are expected to be more important. In this paper, we investigate new green water challenges associated with the Santos Basin. We employ an engineering prediction tool, KINEMA, designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in early design load analysis. We perform a sensitivity study to arbitrary wave directions and present preliminary results from a case study that would be illustrating for the Santos Basin. Firstly, a comparison between numerical green water predictions and a set of earlier model test data for a Campos Basin case shows satisfactory agreement. A sensitivity study suggests that an empirical tuning factor, which is related to wave amplification and wave-structure interaction, should decrease with increasing wave heading. Then, a preliminary numerical investigation of the green water problem in Santos Basin wave conditions demonstrates that although the wave impact from the largest waves (S-SW) may be avoided by heading the vessel towards S-SW, other wave directions have to be taken into consideration. The results presented herein confirm that multi-directional wave heading is a green water challenge in the Santos Basin. Further studies that address this problem in detail, in special variations in the wave-structure interactions due to wave heading, and for actual particular Santos Basin FPSO’s, are recommended.

Irregular Wave Loads on a Gravity Based Foundation in Shallow Water

2011 ◽  
Author(s):  
Erik D. Christensen ◽  
Iris P. Lohmann ◽  
Hans F. Hansen ◽  
Piet Haerens ◽  
Peter Mercelis ◽  
...  
Keyword(s):  
Time Series ◽  
Shallow Water ◽  
Wave Breaking ◽  
Wave Loads ◽  
Wave Load ◽  
Foundation Design ◽  
Wave Condition ◽  
Irregular Wave ◽  
Run Up ◽  
Wave Induced

In order to achieve a safe but cost-effective foundation design of offshore structures, it is important to include effects of run-up and wave breaking in the estimation of wave loads on structures in relatively shallow water. This study presents results from a method applied to estimate wave loads on a gravity based foundation (GBF) coming from irregular waves which are potentially subjected to wave breaking. The objective of the study is to analyse the loads on gravity based foundations for wind turbines on the Thornton Bank, Belgium, due to irregular breaking waves. This study focuses on uncertainties in estimation of maximum loads based on the same wave condition, i.e. (Hs, Tp, Wave Spectrum). To this end three different synthetic irregular wave time series elaborated from the same wave condition are used to simulate the wave load on the GBF. The simulations result in time-series of wave loads and wave elevations on the GBF. The loads obtained from the model indicate a small difference (below 10% in peak values) between the wave-induced inline force for the three simulations, and differences up to 15–20% on the peak values of the obtained wave induced overturning moments. From the simulation results it is also possible to investigate flow patterns and run-up around the structure.

CFD Analysis of a LNGC Carrier in Waves

2012 ◽  
Author(s):  
Emmanuel Guilmineau ◽  
Alban Leroyer ◽  
Michel Visonneau ◽  
Emmanuel Ory
Keyword(s):  
Oil And Gas ◽  
Model Tests ◽  
Product Line ◽  
Irregular Waves ◽  
Head Wave ◽  
Linear Potential ◽  
Cfd Simulations ◽  
Wave Condition ◽  
Numerical Predictions ◽  
Cfd Method

Single Buoy Moorings (SBM) Offshore is a pioneer in the offshore and gas industry. Its product line is the supply of facilities and services for the development and production of offshore oil and gas fields as well as the systems relevant to the mooring technology at large. SBM is currently developing various concepts aimed at offloading LNG (Liquefied Natural Gas) carriers offshore. These concepts whether they assume tandem or side-by-side offloading have in common a building block: the LNG carrier. Owing to its unusual shape (shallow draft, non wall sided hull at the waterline with a flared bow and a transom stern and the presence of a bulb just below the sea surface) at least compared to standard VLCCs (Very Large Crude Carrier), difficulties arise when performing diffraction calculations and when comparing model test results in monochromatic, bi-chromatic and irregular waves with numerical time domain simulations. The main objective is to identify whether differences between model tests and standard numerical predictions based on linear potential theory can be bridged in increasingly complex wave fields by resorting to CFD simulations. The CFD software used is ISIS-CFD, developed by the Numerical Modelling Group of the Fluid Mechanics Laboratory of Ecole Centrale de Nantes and distributed as commercial software by NUMECA International under the name FINE/Marine. CFD simulations have been performed in monochromatic head wave condition with and without the 4-line mooring system to prevent the LNG carrier from drifting away. The CFD method is described and a comparison between model tests and simulations is presented. CFD shows that it is able to predict the motions measured in model tests. In addition, both the wave frequency and the natural frequency of the mass spring system are correctly linked with the frequencies of the predicted motions.

A Numerical Investigation of Steep Irregular Wave Properties With a Mixed-Eulerian Lagrangian HOS Method

2020 ◽  
Author(s):  
Sébastien Fouques ◽  
Csaba Pákozdi
Keyword(s):  
Computational Cost ◽  
Perturbation Expansion ◽  
Nonlinear Effects ◽  
Irregular Waves ◽  
Extreme Waves ◽  
Wave Impact ◽  
Irregular Wave ◽  
Highly Nonlinear ◽  
Steep Waves ◽  
Steep Wave

Abstract The design of structures at sea requires knowledge on how large and steep waves can be. Although extreme waves are very rare, their consequences in terms of structural loads, such as wave impact or ringing, are critical. However, modelling the physical properties of steep waves along with their probability of occurrence in given sea states has remained a challenge. On the one hand, standard linear and weakly nonlinear wave theories are computationally efficient, but since they assume that the steepness parameter is small, they are unable to capture extreme waves. On the other hand, recent simulation methods based on CFD or fully nonlinear potential solvers are able to capture the physics of steep waves up to the onset on breaking, but their large computational cost makes it difficult to investigate rare events. Between these two extremes, the High-Order Spectral (HOS) method, which solves surface equations, is both efficient and able to capture highly nonlinear effects. It may then represent a good compromise for long simulations of steep waves. Unfortunately, it is based on a perturbation expansion where the small parameter is the wave steepness, and consequently, simulations tend to become unstable when steep wave events occur. In this work, we investigate the properties of irregular waves simulated with a modified HOS method, in which the sea surface is described with a Lagrangian representation, i.e. by computing the position and the velocity potential of individual surface particles. By doing so, nonlinear properties of the surface elevation are simply captured by the modulation of the horizontal and vertical particle motion. The same steep wave is then described more linearly with a Lagrangian representation, which reduces the instabilities of the HOS method. The paper focuses on bi-chromatic waves and irregular waves simulated from a JONSWAP spectrum. We compare simulations performed with the standard HOS and the modified Lagrangian methods for various HOS-orders.

Non-Linear Air Gap Analyses of a Semi-Submersible Compared With Linear Analyses and Model Tests

2014 ◽  
Author(s):  
Jørgen Kvaleid ◽  
Volkert Oosterlaak ◽  
Tor Kvillum
Keyword(s):  
Simulation Model ◽  
Power Spectra ◽  
Model Tests ◽  
Air Gap ◽  
Irregular Waves ◽  
Wave Impact ◽  
Time Step ◽  
Extreme Response ◽  
Non Linear ◽  
Local Wave

For semi-submersible units, the magnitude of air gap or local wave impact in the survival condition is a key design driver. Linear analyses are widely used in the industry to predict survival air gap for semi-subs. Large relative motions, leading to large changes in shape of the submerged hull and large changes in water plane area make this approach questionable. In this paper, the GG5000 [1], a twin pontoon four legged semi-sub is considered. Both linear analyses and model tests had been performed, but the results were diverging. It was decided to investigate further, using non-linear hydrodynamic analyses. Initially, the model test setup is reproduced in the numerical model. The simulation model is verified for both response power spectra and extreme response distributions. In the non-linear simulations, the wetted surface of the hull is updated for each time step. Both excitation and restoring forces are based on the instantaneous wetted surface. This proves essential for the prediction of large motions. Later, the verified simulation model is run with realistic full scale setup including elastic catenary moorings with coupled cable dynamics, thruster assist, irregular waves and irregular wind. Highly non-linear effects proven to be vital to accurate air gap prediction are investigated and their representation in the non-linear analyses is validated against model tests.

scholarly journals A NEW DESIGN METHOD OF RUBBLE MOUND STRUCTURES

1986 ◽  
Vol 1 (20) ◽  
pp. 161 ◽  
Author(s):  
Cheong-Ro Ryu ◽  
Toru Sawaragi
Keyword(s):  
Design Method ◽  
Wave Train ◽  
Wave Force ◽  
Irregular Waves ◽  
Wave Condition ◽  
Irregular Wave ◽  
The Mean ◽  
Rubble Mound ◽  
Run Up ◽  
Wave Control

A new design method of rubble mound structures with stability and wave control consideration is proposed, by which the reduction of wave reflection and run-up and increase in rubble stability are assured under the given wave conditions. Wave control and stability increasing functions due to change of the slope shape of rubble mound structures are discussed on the basis of the experimental results for regular and irregular waves. The new design formula developed here considered the allowable percentage of damage and the wave grouping effects on rubble stability using a new assumption of the mean run-sum as an index of the irregular wave force. The run-sum is defined as the energy sum of a run satisfying a critical wave condition and the mean run-sum is the mean of run-sum for a irregular wave train.

Sign in / Sign up

Export Citation Format

Share Document